Plastic bristles are cut to length from a continuous monofilament. Ideally the surface of cut is planar and perpendicular to the bristle axis. However, particularly when cutting bundles, frequently diagonal cuts occur and there may even be burr or flash formation on the surface of cut. For many applications such sharp-edged bristles are unusable or at least undesired. Therefore the ends of the bristles are worked or treated, so as to break the edges and in the ideal case obtain a spherical bristle top.
Essentially three methods are available for working the bristle ends, namely the chemical treatment thereof with suitable solvents, the thermal melting of the bristle ends and mechanical, abrasive working by grinding. In practice, the latter method has been largely adopted. The tool used consists of abrasive disks. This working of the bristle ends takes place on the finished brush on which the bristles are arranged in bundles. So as to be able to effectively treat or work the individual bristle end, the tool working surface on the bristle end must constantly change. This takes place by relative movements of brush and tool in different directions and by a profiling of the tool, or so that at least in the vicinity of the ends the bundles are divided up by spreading the bristles (DE 41 41 372 A1).
Although relatively satisfactory results can be obtained in this way in the case of brushes, whose bristle ends are located on a planar or only slightly curved envelope, this is not the case with circular brushes, particularly with so-called turned circular brushes, in which the bristles are optionally held in several layers between two twisted, central wires and the bristle ends are located on a cylindrical surface or on a conical surface. This construction is e.g. chosen for interdental brushes and mascara brushes due to the necessarily small cross-section of the bristle support, but also for massage brushes, bottle brushes, etc.
It has already been proposed in connection with circular brushes (DE 41 41 372 A1) to rotate the brush in spaced manner between two substantially parallel heating plates or to insert same in cylindrical holes of a heated tool, followed by rotation (EF 438 935 B1). In this case the spacing between the bristle ends and the heated surface, their temperature and the residence time of the circular brush in the tool must be very carefully matched to one another to ensure that the radiant heat is uniformly applied to the bristles. This is not possible in the case of parallel heating plates, because the surface temperature decreases towards the open sides of the tool and is not possible with cylindrical holes, because the heat accumulates in the hole and rises from the hole opening to the hole bottom. The major disadvantage of all thermal working and treatment processes, is the inadequate quality of the work result. The bristle ends must at least be heated to such an extent that the plastic passes into the melted state. It would be desirable if only the cut edge was melted down. However, this is not possible in practice, because such a precise temperature control is impossible. As the bristle diameter is sub ject to fluctuations due to the molecular structure of the plastic monofilament this necessarily leads to a different melting depth. To this must be added that any thermal action leads to the dissolving of the linearly oriented molecular structure. Thickened parts of non-uniform thickness form. In addition, at the bristle end the plastic loses its elastic characteristics, i.e. the bristle end becomes harder and breaks off after a short period of use.
The problem of the invention is to propose a device for the mechanical working of the bristle ends on circular brushes, which permits the manufacture of uniformly rounded bristle ends.